Intermittent P0300 Random Misfire and Stuttering on Acceleration

Question

My truck has started stuttering badly when I try to merge onto the highway or climb a slight grade. The Check Engine light starts flashing under load but sometimes goes solid or turns off when I let off the gas. It feels like a massive loss of power and the whole cab shakes until the RPMs stabilize.

Jordan Lee · Accepted Answer

The issue was a failing High Pressure Fuel Pump located under the intake manifold. The pump was leaking fuel internally into the lifter valley, which also thinned out my oil. I replaced the HPFP (Part #12658481), the high-pressure fuel pipe (which is one-time use), and performed an immediate oil change. The truck now pulls hard with no stuttering and the fuel trims have returned to +/- 3%.

Megan Rivera · Answer

Take a look at your mass airflow sensor (MAF) readings. If the sensor is dirty or failing, it can report incorrect air mass to the PCM, leading to a fueling mismatch that triggers a random misfire code across multiple cylinders.

road_rambler · Answer

Since you have P0172/P0175 rich codes along with the misfire, you should check your high-pressure fuel pump (HPFP). If the internal diaphragm leaks, it dumps raw fuel into the crankcase through the vacuum reference or high-pressure side, causing a rich condition that fouls the combustion cycle.

backyard_bart · Answer

Have you checked your ignition coils? On these LT-based engines, the coils can develop hairline cracks in the plastic housing that only arc over when cylinder pressures are high during acceleration.

Intermittent P0300 Random Misfire and Stuttering on Acceleration

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